Mini Split BTU Calculator
Enter your room size and conditions, get the recommended BTU and standard unit size — plus a checker that tells you if a unit you're eyeing is undersized, correct, or oversized.
Coming soonWood Stove Sizing
Match a wood stove's BTU output and firebox size to your square footage and climate, without the showroom upsell.
Coming soonDehumidifier Sizing
Find the right pint-per-day capacity for a basement, crawlspace, or whole-home setup based on area and dampness.
Why these tools exist
Almost every page-one mini split "calculator" is run by a brand that also sells you the unit. The number you get is rarely neutral, and the math is hidden. Home Systems Sizing does the opposite: an honest, Manual-J-lite estimate with every factor shown, and a clear warning about the most expensive mistake homeowners make — buying too big.
We don't sell equipment. When we link to a product, it's labeled as an affiliate link and it never changes the number the calculator gives you. Our job is the right size; where you buy is up to you.
Start here
- Mini Split BTU Calculator — what size do I need, and will the unit I'm looking at fit?
- What size mini split do I need? Complete BTU sizing guide
- Mini split BTU chart by room size (9,000–36,000 BTU)
Affiliate disclosure · We may earn a commission from qualifying Amazon purchases at no cost to you. Our calculators and guidance are not influenced by any product link.